1. Field of the Invention
The present invention relates to apparatus for measuring the amount of displacement between two elements, and more particularly, to apparatus for measuring the amount of relative displacement of mutually facing electrodes in such a direction as to cause a change in the distance therebetween.
2. Description of the Prior Art
As a displacement measuring apparatus there is already known a tilt meter apparatus for measuring the inclination of a movable electrode with respect to a fixed electrode utilizing the dependence of electrostatic capacity between the electrodes on the distance therebetween. In such known apparatus the electrostatic capacity between the fixed and movable electrodes is utilized as a capacity for determining the oscillating frequency of an oscillator, and the mutual displacement of the electrodes is thus converted into a change in the oscillation frequency to achieve the measurement.
The use of such apparatus has, however, led to difficulties in conducting measurement with sufficient accuracy, as it is easily subjected to external perturbations such as:
(1) fluctuation in oscillation frequency resulting from temperature-dependent changes in characteristic constants of elements such as a transistor constituting the oscillator; and
(2) noise effect on the measurement which is unavoidable since the use of a narrow-band filter is rendered impossible by the use of frequency change as a parameter representing the change in the distance between the electrodes.